Well to be honest, the mains problems they suffer from, other then the lower end models starting to look rather tatty nowadays, is rust in the arches (dont really rust anywhere else), high milages can be prone to HGF although it depends how you drive them as well, drive a high miler nice and it will be nice in return, and the on the auto versions the boxes tend to go after 60,000 - 75,000 miles or so.
Other then this, its general wear and tear, the usuals when buying a car, try and get one with service History
, especially histroy within the last few years so you can gauge things like cam belt changes etc, because maintenance and repairs can be slightly expensive mainly because parts seem dearer, although its not so bad nowadays.
In general, the engines are pretty much bullet proof, I had a Clio with 89,000 on the clock when I got it, but it had almost certainly been clocked at sometime in its life, I rekon it was probably a good 20,000 miles more, but it ran like a dream, I just kept it well serviced, loved it to bits, until a woman crashed into me at a junction.
Out of the 3 I have had, the engines were all sound tbh, on my auto the box went and I couldnt be bothered paying £600+ to get it sorted, my first manual someone crashed into it, the engine was still fine lol, and on my second manual I gave it HGF - it had done 115,000 miles and I in-advertently had a race when the engine was still cold and noticed it chugging like a steam train as I slowed down lol.
An RSi is likely to have been ragged in its life, so if its really high mileage be a bit warey, check everything that you can possibly check.